uplcom driver and USB modem

I've recently been trying to get my USB modem working in FreeBSD
-CURRENT, without much success.   In Linux, I can load the pl2303
driver and a ttyUSB0 device node is then used to communicate with
the modem as if were attached to a serial port.   In FreeBSD, I load
the uplcom driver and the Prolific PL-2303 device is found and a 
ucom0 node gets created, but after that there doesn't seem to be
any communications with the modem.   Is the uplcom driver broken
for my Jetway modem, or is there something I can do to get comms
working?   I know I should probably get a 'proper' serial modem, but
I'd like to know if it's at all possible to get my current modem
working.

--
Bruce Cran